I have a guy in AZ who does a lot of cage engine head porting and has done a few Honda motorcycle heads. I will likely be sending him my head and I will also be installing a little larger valve. I am also considering doing a ceramic coating on the faces of the valves to help with heat.

At the end of the day, I will likely have all of this into a bike that will still be a KLR.

***this is on a pre-08 bike***

If you dont have access to the site, it summarizes that the 685 with a ported head and larger valves nets extra power. Patman went from a stock 34hp to 46hp with a very nice power curve to 6300 rpms. It falls of drastically at about 7100rpms.

Patman says "The 685 kit is a pretty good boost even to a stock bike and has the added benefit of lessening the vibration through a lighter piston. Also the kit I got, and I'm not sure on the production kits ) cut oil consumption by...welll 100% I guess. I haven't used any yet."

KLR Cary who built the engine says "The head is a "Stage-2". That runs about $585.00. The valves are oversize, but will clear even with the stock piston. There are options that can add, or deduct from that price.Â I feel that it is a practical place to stop. There is an afull lot more that can be done to the head, but the returns for the dollar start to fall off steeply. Total cost for both, if you do the assembly is just under $1000

Some other things you shoud know:
The exhaust noise level will increase a good amount, no matter what system your using.
Jetting is more difficult, and what worked before will no longer do. The piston alone won't change it. The head WILL. Slide lift hole must not be bigger than 7/64". The difference in lift hole size makes a much larger change. I'm running a stock size lift hole in mine. It will also require the KLX needle. The DJ needle will work in some situations, but the KLX needle is more likely to make it easier to jet. The stock needle will not work!
Heavier clutch springs are wise. Stock is OK, but borderline, though that depends somewhat on how you use it.